1
High-rise Buildings in Post 9-11 Period
Venkatesh Kodur
Michigan State University
Outline
• The 9/11 Incident
• Background
• Sequence of Events
• Damage Assessment
– Twin Towers
o Features
o Science Behind Collapse
– Other Buildings
• Recommendations
• High-rise Buildings in US in Post 9-11 Period
• Innovations for Improved Performance
• Case Studies - Improved Performance
• Changes in Building Codes
• R& D Activities in Structural Fire Safety Area
Facts – WTC
Excerpt from TIME magazine
WTC complex 7 buildings
Owner Port Authority of NY & NJ
Twin Towers
(N&S)
WTC 1 & WTC 2
Height 110 stories, 1368 & 1362 ft
Total area 12 million sq ft
Capacity 50,000 Employees
Elevators 239
Escalators 71
Rest rooms 1200
Architect,
Engineer &
Contractor
Minoru Yamasaki Assoc.
Skilling, Hellie, Robertson &
Christianson
Tishman Construction Co.
Reputed Firms
Opened April 4th, 1973 Excerpt from Reuters
Twin Towers – High & Mighty
Manhattan Prior to Attack
WTC – Looking Up
Lower Manhattan
September 11, 2001
AA 11, BOS – LAX
Hit N Tower at 8:46 am
UA 175, BOS - LAX
Hit S Tower at 9:03 am
Excerpt from Reuters
The Incident
2
South Tower – Fire Ball South Tower Collapsing
People Fleeing People on Highways
WTC 3 WTC 7
3
NYC – Post 9/11
Before
Attack….
…and
After Attack
NYC Skyline – Before & After
9/11
WTC Disaster
September 11, 2001
• Terrorist attack
– Buildings and infrastructure – disaster
o Colossal damage and destruction
– Building performance / investigation
o Engineering profession
– Building Performance Assessment Team (BPAT)
o 23 member expert team
o Lead by FEMA/ASCE + 15 organizations
o Structural Engg, fire, blast tall buildings,e failure investigations, metallurgy
BPAT – Objectives
• Obtain, record and
preserve perishable
data
• Damage Assessment
• Understand what
happened
• Determine if there are
obvious lessons to
be learned
• Recommend any
needed Code changes
• Recommend more
detailed study
Ground Zero Situation
WTC site visit
• 8-10 Blocks cordoned off, high security
• Fires burning and smoldering
• Dust: breathing apparatus and glasses required
• No power PC buildings
• Safety issues
• Health issues
– Asbestos fire protection
Damage Assessment
• 2830 lives lost
– Fire, Police, rescue personnel (403)
– 880 injured
• Collapse / damage to buildings
– 1/3 of NYC financial district
• Damage to infrastructure
• Total losses – billions of dollars
4
Damage – Buildings
• Collapsed – 4
• Partially collapsed – 4
• Major structural damage – 9
• Minor structural damage – 18
• Needed cleaning – Number of buildings
• Buildings inspected – 406
• Loss of office space – 30 million sq. ft.
• Affected area – 1 to 2 miles radius
New York Financial District
Excerpt from FEMA report
Sequence of Events
3. WTC 2 collapses (56 m), & the
debris hit
Bankers Trust
American Express
Vista Hotel
4. WTC 1 collapses (1h 42 m),
debris hit
Vista hotel, WTC 4, 5, 6, 7
5. WTC 3, 4, 5, 6 collapse (4-6
hrs)
6. WTC 7 collapse (7 hrs)
1. Aircraft strikes WTC 1
at 92-96th floor (8:46 am)
2. Aircraft strikes WTC 2
at 78-84th floor (9:03 am)
7. Damage to other buildings
Collapsed Buildings
4 Buildings
– WTC 1 - 110 stories
– WTC 2 - 110 stories
– WTC 3 - 22 stories
– WTC 7 - 47 stories
Steel framed office buildings
Impact – Major factor
Blast – Minor factor
Structural – Major factor
Fire – Major factor
Progressive collapse
Huge amount of Debris - cleared in 1 year
WTC 1 & WTC 2 – Features
110 stories
Floor plate of 207’ x 207’
40,000 sq. ft./floor
Constructed 1971
Steel framed buildings
– Concrete deck slab
Not Twins - Siblings of same family!
Building WTC 1 WTC 2
Height 1360+ Ant. 1368
Antenna Y N
Core E-W N-S
Wind effects Diff. Diff.
• Innovations
Technical
Services
Technical Services
Technical Services
Skylobby
Skylobby
Underground
Car Park
(total capacity 2000)
110 s
tori
es =
1362 f
t (N
ort
h),
1368 f
t (S
ou
th)
Technical Services
6 s
tori
es
Open Plan Office
Express Elevators
Express Elevators
208 ft
208 f
t
35 ft
60 f
t
Local
Elevators
60 f
t
35 ft
WTC Overall System Design
5
• Gravity loads due to dead
and live loads are carried by
an exterior framed-tube
system and a central core.
• Lateral loads due to winds
(and earthquakes) are
resisted by the exterior
framed-tube only.
• Typical total load =
286,000 tons per floor
Structural steel weighed about 180,000 tons
per tower.
Exterior framed-tube Central core box
columns
60 columns per side
Structural System
Floor slab
Structural Framing
Closely spaced (3’ 3”)
perimeter columns
(tube & spandrel
system)
Rectangular box
columns at core
Long span trusses
support lightweight
concrete fill on metal
deck
2-way framing
at corners
Aluminum Sheet Aluminum Window Frame
Special Tinted Glass
Vermiculite
Plaster
Fire-resistant
Plaster
External
Column
Guide
Rail for
Windo
w
Cleani
ng
Equip
ment
• Code requirement: 2/3 hour FRR
– Asbestos abatement in 80’s – Vermiculite plaster sprayed on outside of steel – Cafco type D, made of ceramic fibers, as fire- resistant plaster on the inside.
• Sprinklered Systems
• Water for extinguishing fires is available in 18,500 liter tanks, installed on 4 technical services floors.
• Occupancy • 25,000 occupants/tower, plus 25,000 visitors
• Over 400 companies in Towers
• Emergency Staircases - 3 Stairwells – A, B, C
• A and C were 112 cm (44”) wide
• Stairwell B was 142 cm (56”)
• All stairs in the Elevator (central) core
• Number of steps between landings varied (probably from 6, 9, 11 and 13 steps)
Fire Protection Features Emergency Stairways in Towers
Effects of Aircraft Impact
• Impact shattered and fractured
2/3 of columns on one face
• Partial collapse of floors occurred at
• Impacted columns
• Debris penetrated building core
– Damaged core columns
– Damaged stair shafts & elevators
• Impact caused failure of fireproofing
in affected area
• Initiated fire
State of Structural System
Impact damage to N face of WTC
1
Impact damage to ext. columns on
N face of WTC 1
6
Excerpt from FEMA report
• Debris
penetrated
building core
• Damage to
core columns
Significance of Impact Structural Analysis
Excerpt from FEMA report
Effect of Fire
• 45,000 liters in each plane
25% Fire balls
25% Shafts
50% Consumed in few
minutes
• Fire size – 3-5 GW
Energy – nuclear plant
• Fire temperatures – 1100° C
Rate of rise of temp
• Ignited several floors
Evacuation of Occupants
• Occupancy of WTC 1, 2
– Sept. 11: 15,000-20,000 people
– Capacity: 40,000 to 50,000 people
• Damaged stair shafts and
elevators
• Virtually all fatalities were located on
impact floors or floors above
– Only 16 (4) occupants from impact
floors or above survived
– 99% of occupants below impact
floors survived
Role of Fire Issues
South Tower Collapsing
• State of the structural
system
• Fire growth
- Jet fuel
• Fire proofing
• Active fire protection
• Fire fighting
• Performance of structural
Collapse of WTC 1 & WTC 2
7
Performance of Structural Elements
Impact caused failure of
fireproofing on structural
elements
• Damage much more in trusses
• Floor trusses relatively flimsy
– difficult to fire protect
• Connections played crucial role
Effect of Fire on Steel
Steel when heated
– Expands
– Looses flexural rigidity
– Looses strength
Increased demand
Reduced strength
Excerpt from FEMA report
Collapse Mechanisms
Excerpt from FEMA report
Floor System Failure Instability of Columns
(Longitudinal Unsupported
Lengths)
North tower: Hit at 8:46 AM
Collapsed after 1 hour, 42
minutes
Ab
ou
t 0
.79
H
South tower: Hit at 9:03 AM
Collapsed after 56 minutes
78th to 82nd floor
84th to 93rd floor
Point of
impact: close
to the corner
and with an
angle
South face
Ab
ou
t 0
.87
H
90th to 95th floor
North face
Point of
impact:
close to the
center and
nearly
normal to
the building
96th to 103rd floor
Collapse Contradictions Successful Evacuation
Reasons for Low Fatalities
• Low occupancy
• Overall good conditions on floors and stairwells
• Limited delay to start evacuation
• Occupants remained calm
• Past experience from 1993 evacuation
• Improvements after 1993 Bombing
• PLM paint on stairs and handrails
• Fire Safety Teams in WTC complex
• Fire Drill every 6 months (since 1993)
• Rescuers &co-workers helped disabled & injured
• Robustness of Towers
5000 to 7000 people in each tower (USA Today) - (1/4 at work)
• Election day in New York
• First day of school
• People start work at 9:00-9:30 AM
Fatalities - Total Numbers (USA Today – Dec. 19
01)
Tower 1 (1,431) 1,259 fatalities above 92nd floor 72 died on 91st floor and lower
Tower 2 (599) 597 fatalities above 78th floor 2 died below 78th floor (4 died)
479 workers (403 rescuers: 343 fire, 37
police)
157 in 2 airplanes
147 guards, delivery people, day workers
10 bystanders outside
• 880 injured
Collapsed Buildings – WTC 3
• WTC 3 – Vista WTC Hotel
– 22-storey steel-framed bldg – 6-storey below sub-grade – 64 x 330 ft. in plan
• 1993 WTC bombing slab collapse
• Arrested progressive collapse survived debris from WTC 2
• Evacuation - WTC 2 to
lobby
• Local collapse – 22 to 7
stories
did not spread
• Full collapse – WTC 1
Collapsed Buildings – WTC 7
47-storey steel framed bldg
– Floors 1- 6
– Con Edison sub-station
– Emergency generator
– 91,000 litres of diesel fuel storage
Fires initiated after WTC 2 collapsed
– Floors 7- 47: offices
– Burned uncontrolled for 8 hours
– No suppression (pressure in water mains significantly reduced after collapse of WTC 1, WTC 2)
– Collapsed at 5.20 pm(~ 7 h after
WTC 1)
– Failure of critical elements – Transfer trusses
8
4 Buildings • WTC 4 – 9 storey
• WTC 5 – 9 storey
• WTC 6 – 8 storey
• Winter Garden – glass & steel barrel vault
– One of the largest covered public spaces in
NYC
Steel framed office buildings
Fire – major factor
Structural – major factor
Impact (debris) – factor
Tensile membrane action – Cardington tests
To be demolished
Partially Collapsed Buildings
WTC 5
WTC 6
9 buildings
• 90 West – 24 stories
• AMEX – 50 stories
• VERIZON – 30 stories
• Merrill Lynch – 44 stories
• Bankers Trust – 40 stories
Steel framed office buildings
Structural – major factor
Impact (debris) – major factor
Fire – not a major factor
Under repair / renovation
Major Damaged Buildings
Bankers Trust
Arrested
progressive
collapse
22nd to 8th floor
View from 16th floor
18 buildings
• 1 Liberty street – steel – 54 stories
• Fed PO building – steel – 30 to 40
stories
• Millennium (Hilton) – concrete – 30 to
40 stories
• 124 Liberty Street – Fire station
Office / hotel buildings
Fire – not a factor
Structural damage – minor
Broken glass, debris
Under repair / renovation
Moderate Damaged Buildings
Subway system • Closed in the area
• Access to stations damaged
• Foot bridge (North) – (WG to
WTC 7)
• St. Nicholas Greek Orthodox
Church
Slurry wall • Waterproof barrier used to
hold water and earth
• Gas / water / power / telephone grid
• Roads, pavement
Affected area – 2-3 km radius
Damage – Infrastructure
New York Financial District
7-storey
basement
(slurry wall)
Subway
Rescue & Recovery – Ground Zero Rescue and Recovery
Debris removal • Land-fill, scrap yards
• Trucks
– Barge (Hudson river)
1.5 to 2 million tons of debris • 150 000 to 200 000 tons
removed (Oct.10)
– Steel recycled as it arrived
Access was restricted
9
BPAT Report - Recommendations • Aircraft impact – extreme events
• Fire-proofing materials – adhesion, cohesion
• Egress systems – staircases • location, number, impact resistant
• Robustness of structural framing
• Minimize progressive collapse
• Connections – fire performance
• Sprinklers – effectiveness, water supply
• Design for fire • integrate design process
• interaction of professions
• Emergency preparedness
• Follow-up Studies - NIST
- WTC 1, 2, 7
- Data & samples
Report - 300 pages, 8
Chapters, 9 Appendices
www.fema.org
WTC Disaster – High Rise Buildings in
Post 9-11 Era
Sept. 11 Incidents
• Performance demands
– Built infrastructure
• Tall buildings
– Critical for commerce, trade
o Concern of occupants
o Drop in real estate value
• Innovations
– Enhance safety
– Minimize damage / collapse
o Cost-effectiveness
o Current Building Practice
51 51
Fire – Severe Hazard & Threat
• Fires cause thousands of deaths & billions of $$ of damage yearly
• 2011 Data – Fire Losses in USA – 1,389,500 fire incidents (4.4% increase over 2010) – 3005 fire deaths (one every 208 min), 17,500 injuries (one every 30 min) – $11.7 billion property losses – Total cost > $50 billion – Residential fires are the most significant – A fire occurs in a structure at the rate of one every 65 seconds – 84% of fire deaths, 27% of fires, 60% of the total $ loss
• Fire represents most severe condition, and can occur as:
– Primary event – natural origin (e.g., lightning, accidental) – Secondary event - Post EQ, blast, explosion, impact
• Fire risk be mitigated through conscientious design & maintenance
– It is impossible to prevent ALL major fires
• Fire safety depends on numerous factors – Fire prevention, suppression & extinction – Successful evacuation of occupants – Structural fire safety – Fire resistance
• Provisions in fire safety measures is critical for:
– Safe evacuation of occupants & fire personnel – Minimize property damage – Control spread of fire – Public Safety, Homeland Security & Economic Activity
52
Improvements in Building Features
– Safety and Security
Oakland Bridge Collapse
Structural features: 1. Strengthening of elevators core.
2. Resilience/Progressive collapse (removal of columns).
3. Strengthening of connections (adding thick plates).
4. Composite construction.
Materials: 1. Use of concrete/masonry in place of gypsum boards (LWC)
2. Additional detailing for fire insulation.
Fire protection features: 1. Back up water supply for fire fighting & Sprinklers.
2. Enhanced stair width (44” to 52”).
3. Improve design of stairs – PLM Paint.
4. Stairs – more exit points to street
5. Regular evacuation drills.
6. Thicker fire proofing (& periodic inspection).
Security features: 1. Enhanced communication system (Signal amplifiers/radio).
2. Air intake for ventilation off ground level/inaccessible.
3. Chemical/Biological filters for air intake
4. Entry restrictions.
5. Sandwich glass for windows – prevent fragmentation.
6. Specific Command center.
7. Thickened concrete core at lower floors.
Emergency and Rescue Procedures: 1. Owner, Municipal, State and Federal levels
53
CIBC Building – General Information
• Building: CIBC Building
• Location: 300 Madison Avenue, NYC
• Stories: 38
• Construction started: 2001
• Estimated completion: 2003
• Cost: $300 million
• Floor area: 1,200,000 sq ft (111,484 m2)
• Height:
• Roof: 575 ft (175 m)
• Elevators/Escalators 26/7
• Occupancy Office/hotel/condos
54
CIBC Building – New Features (Safety &
Security)
Oakland Bridge Collapse
New Safety and Security Features: 1. Box section for columns (instead of H sections)
2. Improved connections (thicker plates to stiffen flanges)
3. An additional hour of fireproofing for all members (+1 hour >
required by NYC building code).
- Additional costs of $4 mill. in lower-column fireproofing
and structural connection improvements.
4. Security film (laminating glass) on windows of floors 2
through 8 (sandwich window glasses).
5. Additional sprinkler riser (system).
6. Triple-wide staircases at trading floors.
7. 60,000-gallon make-up water tank that would go into
operation in the event of a loss of city water
8. Domestic water tanks holding 24 hours of additional storage
for the trading floors.
9. Emergency back up power for all life support and critical
functions equipment to provide a max. power of 10,250 KW
10. Camera surveillance encircling the perimeters and in all
elevators
11. Computerized access to building/parking entries.
10
55
7 WTC – General Information
• Building: WTC-7
• Location: Lower Manhattan in NYC
• Stories: 52
• Site: 250 Greenwich Street, NY.
• Construction started: 2002
• Completion: 2006
• Cost: $700 million
• Floor area: 1,700,000 sq ft (160,000 m2)
• Height:
• Roof: 743 ft (226 m)
• Top floor: 679 ft (207 m)
• Elevators/Escalators 29
• Main contractor: Tishman Construction
• Architect: David Childs (Skidmore, Owings & M.)
• Developer: Silverstein Properties
• Structural engineer: WSP Cantor Seinuk
•The building was promoted as the safest skyscraper in the U.S.
• The building was the first commercial office building in NY to receive the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) certification (gold rating)
56
7 WTC – New Features (Safety and Security)
Oakland Bridge Collapse
New Safety and Security Features:
1. Tower built with redundancy in the steel frame.
2. Two-feet-thick concrete core (f’c is 10,000 psi), floor slabs ranging
8-14 inches thick and walls are 12-27 inches thick.
3. Super fireproofing material for steel members.
4. 20% wider and better-lit stairs, more ground-level exits, emergency
generators, and a redundant emergency command center.
5. Elevators, utilities infrastructure, and exit stairs encased in vertical
(concrete) core.
6. Twice (dual standpipes) the required water-storage capacity for the
sprinkler system
7. Pressurized ventilation to filter out air contaminants.
57
Trump Tower – General Information
• Building: Trump Tower
• Location: Chicago, IL.
• Stories: 92
• Site: 401 N. Wabash Ave. Chicago, IL.
• Construction started: 2005
• Completion: 2009
• Cost: $847 million
• Floor area: 2,600,000 sq ft (240,000 m2)
• Height:
• Roof: 1,389 ft (423 m)
• Main contractor: Bovis Lend Lease
• Architect: Adrian Smith, Skidmore & OM.
• Developer: Trump Organization
• Structural engineer: William F. Baker
• Became the second-tallest building in the Western Hemisphere
58
Trump Tower – New Features (Safety and
Security)
Oakland Bridge Collapse
New Safety and Security Features:
New Safety and Security Features:
1. Height reduced from 136 to 92 floors.
2. Steel framing changed to concrete framing.
3. Extensive use of concrete makes the building more fireproof.
4. Wider staircases.
5. Use of HSC for structural members.
6. Use of SCC for explored matt foundation.
7. Use of Refugee floors (Blocks smoke/fire).
59
One WTC – General Information
• Building: One WTC (Freedom Tower)
• Location: Lower Manhattan in NYC
• Stories: 105
• Site: NW corner of WTC site, (old WTC 6)
• Construction started: April 27, 2006
• Estimated completion: late 2013 or early 2014
• Cost: $3.1 billion ($1,150 per square foot)
• Floor area: 2,600,000 sq ft (241,548 m2)
• Height:
• Antenna spire: 1,776 ft (541.32 m)
• Roof: 1,368 ft (417 m)
• Top floor: 1,314 ft (401 m)
• Elevators/Escalators 70/9
• Main contractor: Tishman Construction
• Architect: David Childs (Skidmore, Owings & M.)
• Developer: Port Authority of NY and NJ
• Structural engineer: WSP Cantor Seinuk
• Owner: Port Authority of NY and NJ
Oakland Bridge Collapse
60
One WTC – New Features (Structural)
New Structural Features: • Steel-Concrete composite framing
• Structure is designed around a strong, redundant steel moment outer core frame consisting of beams & columns through a combination of welding and bolting.
•The moment frame lends substantial rigidity and redundancy to the overall building structure while providing column-free interior spans for maximum flexibility.
• Core is of cast-in-place, RC construction.
• Use of HSC for columns in the inner core (83-97 MPa)
• Provision of blast resistance.
• Extra-strong 1m concrete casing protecting central section
• Reinforced, window-less base.
• These features minimize progressive collapse.
Oakland Bridge Collapse
11
61
One WTC – New Features (Safety and
Security)
Oakland Bridge Collapse
New Safety and Security Features:
1. Air intake to Towers through special “suction
machines” that are high-up (where the air is
clean) and equipped with Biological &chemical
filters throughout its ventilation system.
2. Central upright section equipped with key
safety features, including water-proof lifts, and 1
out of 3 staircases, reserved for firefighters.
3. Extra-strong (1 m) concrete casing protecting
the central section of sprinklers.
4. Sandwich glass panels to protect from
blast/explosions .
62
One WTC – New Features (Safety and
Security) New Safety and Security Features:
Special technology will keep any smoke out.
• Central section will also contain lifts, made water-proof to prevent
damage from water sprinklers, & 2 escape staircases.
• Stairs have 4 street-level exits allowing a quicker escape
• Special fire proofing systems
• Extra-wide, pressurized stairwells (20% wider than code requirements)
Security:
• All vehicles will be screened before entering the site via the underground roadway, including for radioactive materials.
• Visitors to the 9-11 memorial will undergo airport-style screening
• 400 closed-circuit surveillance cameras to placed in and around the site, with live camera feeds being monitored around the clock by the NYPD
• A computer system will use video-analytic computer software designed to detect potential threats such as unattended bags and retrieve images based on descriptions of terror or other criminal suspects
• NYC and Port Authority police will patrol the site
Oakland Bridge Collapse
63
Post 9/11 Changes in Building
Codes/Standards
Oakland Bridge Collapse
IBC (2012) New Safety and Security Features
1. Use of impact resistant materials in the construction of staircases
and elevator shaft.
2. Inclusion of more stairwells or wider stairwells in buildings.
3. Marking the egress path, doors and stairs with photo-luminescent
paints.
4. Work with the Department of City Planning to exclude floor area of
"fire towers" from Floor Area Ratio (FAR) calculations to encourage
their use.
5. Controlled inspections to ensure that fireproofing is fully intact.
6. Require all high-rise commercial buildings over 100 feet without
automatic sprinklers to install sprinklers.
7. Install fire-protected (up to 45 min) and structurally hardened
elevators and fire service access elevators for fire fighters.
8. Develop/use of new fire resistive coating and protection materials.
9. Passive fire protection measures should demonstrate post-event
effectiveness
64
Oakland Bridge Collapse
ASCE-7 (2005) Minimum Design Loads for Buildings and Other Structures:
Loading for fire design wfire = 1.2wDL + 0.5wLL
ACI 216.1 (2007) Code Requirements for Determining Fire Resistance
of Concrete and Masonry Construction Assemblies:
Provisions for mitigating spalling in HSC
Tie configuration for HSC columns
Use of PP fibers
SFPE Fire Standards (2003): Design fire for structural fire design
Thermal analysis of structural members
Structural analysis analysis of structures
AISC-LRFD Manual (2011/2016):
HT material properties of steel (EC3)
Some calculation methods for fire resistance
NYC Building code:
Wider stairs & better designed (PLM paint)
Additional fire proofing (+1 hr)
Regular evacuation drills
Conventional Improved
Changes in Building Codes/Standards - Post
9/11 era
65
Research in Structural Fire Safety Area in
US
• Prior to 9-11, no major research programs in US universities in structural fire safety.
• Number of faculty initiated fire research in structural fire safety.
• MSU, UTA, Princeton Univ., Purdue Univ.
• NIST – WTC Investigation
• NIST – NRFL facility
• Numerous fire safety related
workshops/meetings.
• Fire Safety in Infrastructure
MSU structural fire test furnace
66
Fire safety in infrastructure
Recent Bridge/Tunnel fires:
• I-580 freeway at MacArthur Maze interchange, Oakland, CA (April 29, 2007 ): Fuel tanker transporting 32,500 litters of fuel overturned under the
bridge. Intense heat (temp. around 1100˚C). Strength & stiffness of steel girders deteriorated leading to large
deflections. Significant fire induced forces in girders & connections led to partial
collapse in 22 min. Losses estimated at $9 million.
• I-95 Howard Avenue Overpass, Bridgeport, CT (March 23, 2003): Collision between a car & a fuel tanker transporting 50,000 liters of
heating oil. Fire lasted for two hours & the temp. reached about 1100˚C. Fire caused significant buckling of steel girders & partial collapse of
steel girders. Fire damage costed $11.2 million
• I-75 Expressway near Hazel Park, MI (July 15, 2009 ): Fuel tanker carrying highly flammable fuel crashed into a truck. Steel girders weakened & collapsed in 20 min. The collapse of the overpass caused significant losses & traffic delays
• CA Tunnel – (October 12, 2007)
550 ft long tunnel
Burned for 7 hrs – 1400˚C
Severe damage – Spalling of concrete
MacArthur Maze interchange
I-75 Expressway
12
67
MSU-Princeton Project on Fire
mitigation in Steel bridges
Oakland Bridge Collapse
Euro Tunnel
An approach for classification of bridges for fire risk
o 4 risk grades; low, medium, high & critical.
An approach for modeling response of bridges exposed to fire
An approach for evaluating residual strength of fire damaged bridge
(girders)
Guidelines for mitigating fire risk to steel girders
12.2 m
Concrete slab of 0.20m thickness Steel girder (W33x141)Stiffener (16mm thickness) Loading
68
Approach to Evaluate Importance
Factor
Oakland Bridge Collapse
Euro Tunnel
Risk
grade
Overall class
coefficient (λ) Importance factor (IF)
Critical ≥0.95 1.5
High 0.51-0.94 1.2
Medium 0.20-0.50 1.0
Low <0.20 0.8
Table 1 Risk grades & associated importance factors
for fire design of bridges
Fire risk associated with bridges is grouped into four grades namely low,
medium, high & critical.
About 5% of bridges fall under “critical” risk category.
Vulnerability of bridges in “critical” or “high” fire risk category, can be
minimized by providing fire protection to structural members.
Geometrical features , material
properties & design
characteristics
44%
Traff ic demand
11%
Hazard (f ire) likelihood
23%
Economic impact 13%
Expected f ire losses
9%
Contribution of different classes
(factors) to the overall importance
factor
69
The National Fire Research Laboratory
(NFRL)
• No facilities for experiments on real-scale structural systems under realistic fire & mechanical loading in controlled laboratory conditions.
• NFRL is a unique facility & will enable experiments on the performance of structural elements, subassemblies, and systems exposed to fires up to 20 MW and will contribute to the technical basis for performance-based design methodologies for structures exposed to fire.
• Will allow structures, ranging in size from small components to large systems up to 2 stories in height 9 m (30 ft) and 2 bays × 3 bays in plan, to be tested under fully-developed building fires up to 20 MW using natural gas, liquid hydrocarbons, wood cribs, or actual building contents.
• The test area will consist of a 486 m2 (5400 sq ft) strong floor with multiple anchor points and a 9 m (30 ft) high strong wall
70
The National Fire Research Laboratory
Specifications / Capabilities:
• Strong Floor
• 18.3 m x 27.4 m (60 ft x 90 ft) post-tensioned floor with full basement
• 9 cell RC box girder with 406 mm (16 in) thick shear walls at 3.0 m (10 ft) o.c.
• Basement ceiling height: 2.7 m (9 ft)
• Floor thickness: 1.07 m (3 ft-6 in) with 152 mm (6 in) sacrificial top surface
• 1218 anchor points on 0.61 m x 0 61 m (2 ft x 2 ft) grid (sleeves or anchors)
• Load per anchor point: 445 kN (100 kips) up or down
• Shear capacity per anchor point: 222 kN (50 kips) (at top of slab)
• Moment capacity per anchor point: 136 kN-m (100 ft kips) (at c.g. of strong floor)
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The National Fire Research Laboratory
Specifications / Capabilities:
• Strong Wall
• 9.1 m high x 18.3 m wide (30 ft high x 60 ft wide)
• 1.2 m (4 ft) deep post-tensioned concrete wall
• 420 anchor points on 0.61 x 0.61 m (2 ft x 2 ft) grid
• Horizontal Load 146 kN/m (10 kips per lineal ft) at 9.14 m (30 ft)
• Environmental control system (ECS) Hood and Pollution Control System
• 13.7 m x 15.2 m (45 ft x 50 ft) steel hood
• Height above floor: 12.5 m (41 ft)(excluding skirts)
• ECS maximum sustained capacity: 20 MW
• ECS maximum flow rate: 5100 m3/min (180,000 cfm)
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The National Fire Research Laboratory
Specifications / Capabilities:
• Cranes
• Two 178 kN (20 ton-force) bridge cranes (sharing single set of rails)
• Height of rails above floor: 11.2 m (36 ft-8 in)
• Clearance, bottom of bridge-to-floor: 9.8 m (32 ft)
•Configurable Hydraulic Loading System
• Hydraulic Power Unit 340 lpm (90 gpm)
• Actuators (double acting) 762 mm (30 in)stroke w/ servo valve, load cell, and swivels
• Eight 240 kN (55 kip) Tension, & 365 kN (80 kip) Compression
• Two 445 kN (100 kip) Tension, & 650 kN (145 kip) Compression
• Two 956 kN (215 kip) Tension, & 1470 kN (330 kip) Compression
• Four hydraulic service manifolds
• Controller
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